Portable drafting device



Filed April 4, 1968 4 Sheets-Sheet 1 \JNVENTOR.

JOHN SHAPIRO ATTORNEY Oct. 14, 1969 J, sH P RO 3,471,930

PORTABLE DRAYTING DEVICE Filed April 4, 1968 4 Sheets-Sheet 2 INVENTOR JOHN SHAP IRO ATTORNEY Oct. 14, 1969 J. SHAPIRO 3,471,930

PORTABLE DRAFTING DEVICE Filed April 4, 1968 4 Sheets-Sheet 5 INV EN TOR. JOHN SHAPIRO AT TORNEY Oct. 14, 1969 J. SHAPIRQ 3,471,930

PORTABLE DRAFTING DEVI CE Filed April 4, 1968 4 Sheets-Sheet JNVENTOR JOHN SHAP IRO ATTORNEY United States Patent 0 3,471,930 PORTABLE DRAF'HNG DEVICE .iohn Shapiro, Coral Gables, Fla, assiguor of fifty percent interest to Mahmut I. Goench, Queens Village, N.Y. Filed Apr. 4, 1968, Ser. No. 718,891 Int. Cl. B431 11/00 US. CI. 3327 12 Claims ABSTRACT OF THE DISCLOSURE connected to shift the stylus along the body portion by a differential driving connection so that a plurality of different functions may be simultaneously imposed on the stylus, and the stylus will thus move in a direction and for a distance dependent upon the algebraic sum of the functions imposed.

BACKGROUND OF THE INVENTION Field of the invention This invention is in the field of drawting instruments, and particularly cam drafting instruments.

Still more particularly, this invention is in the field of a portable drafting instrument capable of drawing the rise and fall components of circular cams, particularly cams of the cycloidal or spiral type.

The prior art As is well known, circular cams including rise and fall peripheral portions have many industrial applications. The rate of rise and/ or fall of the slope portions of the cams has been found to be critical to optimum driving of the cam follower. For example, a circular cam having a cycloidal configuration is frequently employed for use in follower lift mechanisms wherein it is desired that an initial slow rise be imparted to the follower, the rate of rise progressively increasing throughout parts of the selected cam angle and decreasing throughout other parts thereof.

As is well known, the cycloidal cam function is derived by superimposing a linear function and a harmonic function, the harmonic or sine being typically applied in an initial subtractive sense, a subsequent additive sense and a final subtractive sense.

Another cam function frequently employed is the socalled linear or spiral cam function, the latter often being utilized to return a follower to an initial position from which it had been lifted by the cycloidal cam surface.

A further frequently employed cam configuration is the so-called constant velocity cam, which combines elements of cycloidal cam surfaces with interposed spiral cam components.

Heretofore the design of a circular cam embodying one or more of the noted types of functions has been a timeconsuming and imprecise process. The designer, utilizing graph paper or a similar expedient, mathematically calculates a series of points along the cam curve. Thereafter the draftsman connects the points, the connecting line being relied upon as the replica of the cam surface.

Obviously, the extension of a line through two separate points provides no guarantee that the lines in the areas between such points will follow precisely the mathematically correct plot. Thus it will be appreciated that cams "ice formed in this manner are, at best, approximations of an optimum condition.

By increasing the number of calculated points along the cam surface, a more accurate cam surface will result. However, increasing the number of calculations and plotting such increased number of calculations obviously will add to the labor of creating the cam.

As an alternative to the calculation-graphing method of creating cams, certain devices have been created wherein approximations of the cam contours may be directlyobtained. Such devices, however, are exceedingly large and, hence, not portable, expensive, and require that the work sheets be brought to the machine. Moreover, these devices involve complex mechanical linkages. The necessary tolerances between the linkage components of such devices are such as to reduce the accuracy of the cam surface constructed, to a point whereat it is no greater than a cam surface constructed by the plotting method previously described. Moreover, such devices are so large and expensive that their use cannot be justified in a drafting establishment, machine shop or the like where cams of this sort are only occasionally created.

SUMMARY OF THE INVENTION The present invention may be summarized as relating to a light weight, readily portable cam drafting instrument comprising a body portion mounted for pivotal movement across a work or tracing surface about an axis perpendicular to said surface. A stylus or marker assembly includes a depending marker for contacting and marking the surface, the stylus assembly being slidably mounted on the body portion for movement parallel with the surface.

Linear and harmonic cam function generator components are mounted on the body portion, the function generator components being driven by a traction wheel having a depending portion in driving engagement with the work surface, the wheel being rotated by pivotal movement of the body portion about the pivot axis.

The cam function generator components are operatively connected to the stylus assembly by differentials so that the stylus is moved axially of the body portion a distance and direction dependent upon the simultaneous sum and difference functions of the harmonic and linear generators. In other words, in view of the differential connections between the stylus and the generators, the stylus may be urged toward the pivot point by one generator and simultaneously away from the pivot point by the other generator, the absolute movement of the stylus relative to the pivot point being the function of the algebraic sum of the movements imparted.

Preferably, the distance between the stylus and the pivot point may be initially set at different values, thereby to set the maximum or minimum height of the cam. Similarly, the spacing between the traction wheel and the axis of the function generators driven thereby may be varied, to set the cam angle, i.e., the angle of rotation of the finished cam required to complete the camming action on the follower.

It is further possible, by simple adjustments of the device, to disable one or the other of the function generator means so that when the body portion is pivoted about the pivot axis, only one of the function generator means is effective to induce movement of the stylus. Thus, the device may be employed to register the combined harmonic and linear functions, or the linear function alone or the harmonic function alone.

Accordingly, it is an object of the invention to provide a portable, accurate and inexpensive cam drafting device.

It is a further object of the invention to provide a cam drafting device of the type described which is capable of laying out cams of the circular type embodying single or multiple cam functions.

It is a further object of the invention to provide a device of the type described which may be readily converted to vary the cam angle and the beg inning or end radius of the cam.

To attain these objects and such further objects as may appear herein or be hereinafter pointed out, reference is made to the accompanying drawings, forming a part hereof, in which:

FIGURE 1 is a plan view of a drafting device in accordance with the invention;

FIGURE 2 is a side elevational view of the device of FIGURE 1;

FIGURE 3 is an exploded perspective diagrammatic view of the differential drive mechanism;

FIGURE 4 is a magnified section taken on the line 44 of FIGURE 1;

FIGURE 5 is a magnified section taken on the line 55 of FIGURE 1;

FIGURE 6 is a fragmentary magnified side elevational view of the portion of the device between the arrows 6-6 of FIGURE 1;

FIGURE 7 is a magnified sectional view taken on the line 7-7 of FIGURE 1;

FIGURES 8 to 11 are diagrammatic plan views of the successive positions of the device set up to draw a spiral cam;

FIGURES 12 to 15 are diagrammatic plan views of the successive positions of the device set up to draw a cycloidal cam.

In accordance with the invention, there is shown in FIGURE 1 a cam drafting device capable of directly drawing a multiplicity of different cam curves. The device includes an elongated body portion 10 to which the various components of the device are mounted. The components include a central pivot assembly 11, a cam function generator assembly 12 and a stylus assembly 13.

The pivot assembly 11 comprises a grip portion 14 which may be manually grasped by the hand of the user. The grip portion, adjacent its lower end 15, includes a pointed pivot or fulcrum 16 which is sharpened to permit the unit to be embedded in a work surface, such as a drafting table, over which tracing paper or the like suitable for receiving markings of the stylus has been placed. The grip 14 is made fast to the body portion 10 so that when the grip is rotated about the axis defined by the fulcrum or point 16, the body portion will be rotated to describe a plane parallel with the work surface.

The stylus assembly 13, as best seen from FIGURES 1, 4, 5 and 6, comprises a stylus carrier 17 in the form of a block or rider, mounted for axial sliding movement lengthwisely of the body portion 10. To assure accurate lengthwise movement, the body portion 10 is provided with an axially extending keyway slot 18, the rider or carrier 17 including a key 19, which may be in the form of a screw, which projects slidably and upwardly into the keying slot 18. A transverse bore 20 is formed in the rider or carrier 17, slidably to receive the body portion 10. Preferably the carrier 17 and the body portion 10 are fabricated of or coated with nylon, Teflon, low friction metal or the like, to permit axial sliding movement of the stylus carrier 17.

The stylus carrier includes an upwardly directed stub shaft 21, to which shaft is rotatably mounted a drum or pulley member 22. A bushing 23 is preferably interposed between the stub shaft 21 and the pulley 22, the bushing and drum being retained on the shaft with a minimum of play by a snap retainer ring 24.

A stylus bracket 25 is mounted to the carrier member 17 by a locking screw 26. The locking screw 26 extends through an elongated horizontal slot 27 formed in the offset arm 28 of the bracket. A tubular spacer 29 is interposed between the carrier 17 and the arm 28, it being understood that when the screw 26 is tightened, the arm will be compressed between the head of screw 26 and the spacer 29, to lock the bracket against movement relative to the stylus carrier.

The arm 28, adjacent the slot 27, is provided with a graduated scale 30, for purposes which will appear hereinafter.

It will be understood that when the screw 26 is loosened, the bracket 25 will be free to move relative to the carrier 17, for purposes of initial adjustment and for purposes of permitting the device to serve as a spiral cam drafting element, as will be more fully set forth hereinafter.

The bracket 25 includes an angle arm 31 extending parallel to the work surface and carrying the marking element 32 which depends from the arm and engages the work surface. The bracket 25 additionally includes a U- shaped clamp element 33, including opposed arms 34, 35, FIGURE 4, spanned by clamping screw 36. As will be explained more fully hereinafter, one only of the screws 26 or 36 will be tightened, depending upon whether the device is to be used to draw a combination cam, such as a cycloidal cam, or a spiral cam, respectively. It will be understood that when one of the screws is tightened, the other screw must be loosened.

The cam function generator apparatus 12 is best understood by referring to FIGURES 1, 2 and 7. The apparatus 12 includes a traction wheel 37 mounted for rotation about the longitudinal axis of the body portion 10. The traction wheel is located to the side of the fulcrum or pivot 16 opposite from the stylus assembly 13. The traction wheel includes a perimeter band 38 having a high coefficient of friction, suitable material being an elastomer, such as rubber.

The traction wheel 37 is rotatably mounted to a collar 39, the collar being adjustably located along the body portion 10 by lock screw 40 extending through the collar and engaging against the body portion. The traction wheel 37, through an upper peripheral portion of the perimeter member 38, drives the cam function generator disk 41.

The disk 41 is rotatably mounted to cam generator support block 42. The support block 42 includes an axial bore 43, within which the body portion 10 is slidably received. The support block 42 may be located at any selected position relative to the body portion by a lock screw 44 threaded into the block 42 and having an inner tip 45 engaging against the body portion.

Optionally but preferably, a key and slot connection (not shown) is provided between the block 42 and body portion 10, to assure that the axis of the disk trunnion 46 is located in parallel with the axes of stub shaft 21 of the stylus assembly and grip portion 14 of the pivot assembly.

The disk 41, at its inner periphery, is fixed to a drive pulley 47, which drive pulley is rotatably mounted on the trunnion 46, a bushing 48 preferably being interposed between the trunnion and the inner periphery 49 of the pulley 47.

The pulley 47 carries a harmonic generator ring 50 which is free to rotate relative to the pulley 47. A set screw 51 is mounted on the ring and, when tightened, locks the ring to the pulley for rotation therewith. When the set screw 51 is released, it will be understood that the ring is free to rotate relatively to the pulley.

A Scotch yoke mechanism 52 is operatively connected to the generator ring 50. The Scotch yoke comprises a generally U-shaped member having a flat upper face 53 and downwardly directed side legs 54, 55. The generator or Scotch yoke of the illustrated embodiment includes a transversely extending slot 56. A generator drive screw 57 is threadedly connected to the harmonic generator ring 50, the head of the screw lying within the slot 56.

The head of the screw 57 and the slot 56 are dimensioned to permit slidable movement of the head within the confines of the slot. Additionally, a keying screw 58 is threaded into the trunnion 46. A spacer 59 is interposed between the under surface of the upper plate 53 of the yoke and the upper surface of the trunnion 46.

It will be understood that when the screw 58 is threaded upwardly so that its head portion as well as the head portion of the screw 57 lie within the slot 56, the entire yoke portion 52 will be prevented from moving axially with respect to the trunnion 46. Conversely, when the screw 58 is threaded downwardly so that the head lies within the spacer 59, i.e., is cleared beneath the level of the plate 53, the plate will be free to shift axially with respect to the trunnion 46.

From the foregoing description of the cam generator assembly 12, it will be understood that when the device is bodily rotated by rotation of the gripper 14, the traction wheel will drive the disk 41. The rotating disk, in turn, drives pulley 47. If the ring 50 is locked to the pulley 47 by tightening of the set screw 51, the ring as well as the disk will rotate, inducing, by reason of the engagement of the head of screw 57 in the transverse slot 56, a concomitant axial movement of the yoke or harmonic generator 52.

Alternatively, if the screw 51 is loosened and the locking screw 58 is threaded outwardly so that its head, as well as the head of screw 57, lie within the slot 56, the traction wheel will rotate the disk 41 but the harmonic generator 52 will be locked against axial movement relative to the trunnion 46.

From the foregoing it will be apparent that the pulley 47 will always be rotated when the disk 41 rotates and that the Scotch yoke 52. will sometimes be moved axially when the disk is rotated.

It will be further apparent, as more fully explained hereinafter, that when the Scotch yoke is free to shift axially, it will generate a mathematical function which is harmonic in nature, e.g., in the illustrated embodiment a sine Wave. This movement of the Scotch yoke will be more readily understood when it is recognized that, presupposinga counterclockwise revolution of the disk 41 from the pos1tion shown in FIGURE 1, the screw 57 will drive the Scotch yoke 52 to the right during the first 90 rotation of the screw relative to the body portion to the left with the next 180 relative rotation; and to the right for the final 90 relative rotation. Thus, the pulley develops a linear mathematical function and the plate a harmonic mathematical function.

Differential means are employed to communicate the functions generated by the plate 52 and pulley 47 to the stylus. The differential means for communicating the linear function developed by the pulley 47 comprises a rod or bow 60. A wrap 61 has its ends 62, 63 made fast to the ends of the bow 60. As best seen in FIGURE 3, the wrap 61 has a first convolution A circumscribing the pulley 47 and a second convolution B disposed about the drum 22. Optionally but preferably, the diameters of the drum 22 and the pulley 47 are equal at the region engaging the convolutions.

A second bow 64 is made fast to the depending arm 54 of the Scotch yoke 52, as by machine screws 65, 65. A second wrap 66 has its end portions 67, 68 made fast to the how 64 at spaced points along the length thereof, the wrap being tightly convoluted at convolution C about the drum 22.

As will best be observed from FIGURE 3, when the wrap 66 attached to the Scotch yoke is shifted to the right, a rightward movement of the drum 22 in addition to an anti-clockwise rotation of the drum 22 will result. The extent of linear movement, in accordance with known mathematical principles, will be precisely one-half of the amount of movement of the Scotch yoke and how 64 attached thereto.

Similarly, when the pulley 47 is rotated, 21 linear movement is imparted to the how 60, causing axial and rotary components of movement to be transmitted to the drum 22. Thus, for instance, an anti-clockwise rotation of the pulley 47 will induce a leftward movement of the how 60, and anti-clockwise rotation of the drum 22 and a leftward movement of said drum to the extent of one-half of the movement of the how 60.

In order best to illustrate the operation of the device in drawing spiral cams, reference will now be made to FIGURES 8 to 11 wherein only those parts essential to the understanding of the principle of operation are illustrated, for the sake of simplicity.

Since a spiral cam function is a linear function only, it is necessary to set the device so that it responds to the linear function generator 47 only. To achieve this condition, the Scotch yoke 52 is deactivated in the manner previously set forth, i.e., by releasing the set screw 51 and raising the screw 58. The stylus carrier bracket 25 carrying the stylus 32 is permitted to move slidably relative to the rider or stylus carrier 17 by slackening the screw 26. The carrier is made to move with the bow 60 by tightening the screw 36 to clamp the bow within the clamp 33.

In order to set the minimum spiral height, i.e., the low point on the spiral, the spacing between the fulcrum or pivot 16 and the stylus 32 is set. This setting may be effected by tightening the screw 36 after the proper spacing of the parts has been achieved. The set spacing will be referred to as R When the device is rotated in a clockwise direction, as shown in FIGURE 8, about the fulcrum 16, the traction wheel 37 will be rotated by its contact with the work surface, inducing an anti-clockwise rotation of the disk 41. The wrap 61 being, in the spiral sense, the only active wrap, will cause the stylus 32 to move progressively away from the fulcrum 16.

In FIGURE 9 the device has been rotated through a 45 angle, the stylus at this point having reached the second radius R By further rotation through another 45, the stylus has been displaced further from the fulcrum 16, being displaced to the position R In FIGURE 11, the device has been rotated through whereat the stylus is in the position R It will be understood that, by definition, in the generation of the spiral function the dis placement or degree of advance of the stylus from the starting radius is in direct proportion to the degree of rotation.

From the foregoing it will be readily recognized that it is possible to draw any spiral cam with the device. The rate of rise of the spiral may be varied in the device of the present apparatus by varying the spacing of the traction wheel 37 from the pivot point or axis of the disk 41. It will be understood that when the traction wheel is located closer to the axis of rotation of the disk 41, a more rapid cam rise will be experienced, since fewer rotations of the traction wheel will be required to produce more rotations of disk 41 than would be the case if the traction wheel were spaced further from the disk axis.

While the drawing of a spiral cam will normally be effected by clamping the carrier 17 directly to the bow 60, it will be understood that it is possible to draw the spiral function by using the bow 60 to drive drum 22, the Scotch yoke being deactivated as above provided.

Where it is desired to utilize the device for drawing a cycloidal cam, the following initial adjustments are made.

The screw 36 is released to unclamp the stylus bracket 25 from the how 60. Screw 26 is tightened, thus causing the bracket to be clamped to the stylus rider or block 17. On the cam function generator apparatus 12, the set screw 51 is tightened so as to engage the ring 50 with the pulley 47. The screw 58 is threaded downwardly so that the head thereof is cleared beneath the slot 56 formed in the Scotch yoke 52, thus permitting relative axial movement of the Scotch yoke with respect to the pulley 47.

The next step is to set the cam angle, i.e., the angle of rotation of the body member about the fulcrum 16 which is required to define a complete cycloidal cam function. The cam angle is a function of the spacing of the traction wheel 37 from the axis of the pulley 47 and increases in accordance with an increased spacing of said parts. This spacing may be varied by releasing the set screw 40 controlling the position of the traction wheel (or the set screw 44 controlling the position of the cam generator assembly along the body member 10).

Conveniently, a scale 70 may be marked on the body 1 member 10 to permit the proper spacing of these parts for any selected cam angle. It will be understood that the scale 70 may be marked directly in degrees or may be marked empirically and an auxiliary listing may be provided which relates the empiric scale with the selected cam angle.

In connection with the cam angle, it should be understood that the drawing of a cycloidal cam will be completed when the drive screw 57 which is mounted on the pulley 47 completes a 360 circuit about the axis of the pulley 47.

As noted above, the amount of rotation of the device about the fulcrum 16 necessary to cause said pin to complete said rotation will vary, a lesser rotation (and hence a smaller cam angle) being required where the traction wheel 37 is shifted progressively closer to the pivot axis.

The starting radius R of the cycloidal cam is determined by the spacing of the stylus 32 from the fulcrum or pivot point 16, such spacing being readily set by determining the position of the stylus tip 32 on the scale 30 when the screw 26 is tightened.

Assuming that these settings have been effected and that the apparatus is in the position of FIGURE 12, the cycloidal cam is drawn by rotating the body portion clockwise about the fulcrum 16. In the course of such movement, the stylus will trace from its starting point R at cycloidal cam curve which shifts progressively outwardly from the starting radius.

In the illustration of FIGURES 12 to 15, the device has been set up to complete the formation of a cycloidal cam upon a 180 rotation of the body portion. During the rotation, a counter-clockwise rotary movement of the drive disk 41 about its axis will result. In the course of this rotary movement, the wrap 61 will be continuously driven in the direction of the arrow A to induce a progressive linear movement of the stylus away from the axis of rotation 16. However, it will be observed that by reason of the starting position of the drive screw 57, initial rotation of the disk 41 will cause the pin 57 initially to move away from said axis, carrying with it the bow 64 to which is connected the wrap 66 which will be moving in the direction of the arrow A Since the absolute movement of the stylus 32 will be the algebraic sum of the inputs of the wraps 61 and 66 and since such inputs are initially equal and in opposite directions during the first few degrees of rotation about the pivot axis 16, only a very slight outward movement of the stylus will occur. However, as the device continues to be rotated and the pin 57 rides in portions of the slot 56 of the Scotch yoke which are progressively nearer the center of the slot, the subtractive or leftward movement of the bow 64 and, accordingly, the wrap 66, will be progressively less while the rightward movement induced by the wrap 61 remains a constant. Thus, the stylus 32 will move at a progressively more rapid rate outwardly with continued rotation.

In FIGURE 12 the device has been shown, for example, to have been pivoted through 45, at which point the drive pin 57 is in alignment with the axis of rotation of the pulley 47. At this instant of time, the wrap 66 will have no effective leftward or rightward movement and the outward movement of the stylus 32 will be a function purely of the linear quantity developed by the movement of the wrap 61.

With continued rotation from the position of FIGURE 13 toward the position of FIGURE 14, it will be observed that the pin 57 will drive the Scotch yoke in the direction of the arrow A i.e., in the same direction as the movement imparted by the wrap 61. Thus, the cumulative actions of the two wraps will tend to urge the stylus outwardly at an accelerating pace which is a function of the arithmetic sums of the movements imparted by each of the wraps.

In FIGURE 14, wherein the pin 57 has been rotated through 180 relative to the body portion of the device, it will be observed that the pin 57 is at the far extremity of the slot 56 from which it started and upon continued rotation of the device, will impart the maximum outward movement of the stylus.

In movement from the position of FIGURE 14 to the position of FIGURE 15 (a rotation), it will be understood that in the first 45 of such rotation the pin 57 will impart to the Scotch yoke, how 64 and wrap 66 an outward movement, i.e. movement in the same direction as the bow 61 is moving, such outward movement of the wrap 66 being applied at a progressively diminishing rate.

The last 45 of the 90 rotation (i.e., the last 90 of rotation of the pin 57 about the pulley axis) will develop a movement of the Scotch yoke away from the stylus at a progressively increasing rate. Since the pin 57 is preferably aligned essentially with the periphery of the pulley 47, at the completion of the cam, the movement of the stylus induced by the Scotch yoke will exactly counteract the movement induced by the oppositely moving wrap 61. It will thus be seen that the final stages of the cam curve involve little outward movement of the stylus from the fulcrum point 16.

From the foregoing description it is evident that it is a simple matter to draw an accurate cycloidal cam without the requirement of continuously plotting points along a curve.

The formula for plotting any given point on the curve may be derived from the following:

wherein R -=Radius at any point R =Beginning radius A=Cam angle at R (in Radians) X=Total cam angle (in Radians) T=Thow.

It is accordingly apparent that a particular capacity of the device lies in the formation of cam configurations wherein the cam equation comprises a plurality of different functions which are superimposed.

It will be further observed that by changing the configuration of the slot of the Scotch yoke, a cam of dlfi'erent configuration will be defined since such a change would vary the harmonic equation developed by the Scotch yoke.

The device is particularly adapted to draw another widely used cam configuration, namely, a constant velocity cam. A constant velocity cam is formed by first drawing half of a cycloidal cam, thereafter drawing a spiral configuration and finally drawing the last half of the cycloidal cam. It will be readily recognized that to .draw this type of cam, it will be necessary merely to adjust the components of the apparatus after formation of the first half of the cycloidal function and again after the formation of the desired spiral function.

Many other variations and capabilities of the device will be appreciated by those skilled in the art.

Accordingly, the invention is to be broadly construed within the scope of the appended claims.

While the device has been illustrated in conjunction with motion transmitting differentials of the wrap and drum type, rack and gear type drives may be substituted. The wrap and drum drive is preferred, however, since rack drives involves, in addition to greater original cost, longitudinal play factors not found in belt drives.

In the illustrations, the device has been depicted drawing cam curves of progressively increasing diameters. By rotation of the cam drawing device in an opposite direction, the unit may be used to start at the outside or high point of the cam and trace inwardly to the low point.

Having thus described the invention and illustrated its use, what is claimed as new and is desired to be secured by Letters Patent is:

1. A drafting device comprising an elongated body member, pivot means for supporting said body member on a work surface for rotation about an axis normal to said surface, a stylus carrier movably mounted on said body portion including a depending marking member in contact with said surface, a traction wheel rotatably mounted on said body member including a lower peripheral portion in rolling frictional contact with said work surface, cam function generator means movably mounted on said body portion and differential means providing a driving connection with said traction wheel for shifting said stylus carrier along said body portion responsive to movement imparted to said generator means by said traction wheel.

2. A device in accordance with claim 1 wherein said differential means includes pulley means, bow means and wrap means convoluted about said pulley means and stretched by said bow means.

3. A drafting device comprising an elongated body member, pivot means for supporting said body member on a work surface for rotation about an axis normal to said surface, a stylus carrier movably mounted on said body portion including a depending marking member in contact with said surface, a drive wheel rotatably mounted on said body member including a lower portion in frictional contact with said work surface, first and second function generating component means in driving connection with said drive Wheel for generating first and second functions, respectively, responsive to rotation of said wheel relative to said body portion, said component means being operably connected to said carrier member by a differential drive means whereby said carrier is shifted linearly along said body portion a distance and direction which is a function of the algebraic sum of the simultaneous outputs of said first and second function generating means.

4. A device in accordance with claim 3 wherein said generator means includes a drive disk mounted for rotation about an axis normal to said surface and driven by said wheel.

5. A device in accordance with claim 3 wherein said first and second function generating means generate linear and harmonic functions, respectively.

6. A device in accordance with claim 4 wherein said second function generating component comprises a drive pin operatively connected to said drive disk and displaced from the axis of rotation of said disk, a yoke mounted for slidable movement parallel with said carrier member, said yoke including a slot portion within which said drive pin is slidably disposed.

7. A device in accordance with claim 6 wherein said pin is displaced from said axis of rotation of said disk a distance equal to the radius of said drum.

8. A device in accordance with claim 4 wherein said first function generating component comprises a pulley fixed to said disk, a drive wrap looped about the periphery of said pulley, a drum rotatably mounted on said carrier member, and a wrap convoluted about said drum and pulley.

9. A cam drafting device or the like comprising a body member, pivot pin means depending from a medial portion of said body member for rotatably connecting said body member to a work surface, stylus carrier means linearly slidably mounted on said body member and including a depending marking member, traction wheel means rotatably mounted on said body member including a depending portion for rolling contact with a work surface, a cam generator disk rotatably mounted on said body member and having a surface portion in driving contact with said traction wheel means, linear function generator means operably connected with said disk for movement a predetermined distance and direction in accordance with the direction and .degree of rotation of said disk, harmonic function generator means operably connected with said disk for movement a predetermined distance and direction in accordance with the direction and degree of rotation of said disk, and first and second differential means operably connecting said stylus carrier means with said linear and harmonic function generator means respectively for shifting said carrier axially of said body member a distance and direction in accordance with the algebraic sum of the outputs of said linear and harmonic function generator means.

10. A device in accordance with claim 9 wherein said traction wheel means is adjustably movable toward and away from the axis of rotation of said cam generator disk, thereby to set the cam angle described by said marking member.

11. A device in accordance with claim 9 wherein said differential means each comprise a bow and wrap member axially movably connected to said linear and harmonic function generator means, said wrap members each being convoluted about drum means mounted on said stylus carrier means.

12. A device in accordance with claim 9 wherein said harmonic generator means may be decoupled from said stylus carrier means whereby said carrier means is shifted responsive to said linear function generator means only.

References Cited UNITED STATES PATENTS 1,326,696 12/1919 Simmons.

FOREIGN PATENTS 43 8,694 12/ 1926 Germany. 263,412 12/ 1926 Great Britain.

HARRY N. HAROIAN, Primary Examiner 

